#include<stdio.h>
#include<string.h>
#include<stdlib.h>


int f(int n){
    int i;
    int sum = 0;
    if(n ==  1){

        return 1;
    }
    for(i = 1;i < n; ++i){

        sum += f(n-1);
    }
    sum++;
    return sum;
}

int
main(int argc,char * argv[]){

    if(argc < 2){

        printf("need one positive integer.\n");
        return EXIT_FAILURE;
    }
    int n = (int)strtol(argv[1],NULL,10);
    if(n < 0){

        printf("need one positive integer.\n");
        return EXIT_FAILURE;
    }
    printf("f(%d) = %d.\n",n,f(n));
    return 0;
}